The present invention relates to a bending device for thin-walled metal tubes made of a straight tube guide, a core template, which adjoins the tube guide and is pivotable in relation thereto, having a connection strip, and a mandrel, having a mandrel tip, which is flexible in the region of the core template, and a mandrel shaft, which adjoins the mandrel tip and is rigidly connected thereto and is axially fixed in the tube guide.
Bending devices of this and similar types for thin-walled tubes are known (the magazine “Werkstatt und Betrieb” 104 (1971) 4, pp. 271 to 274, “Verhinderung von Faltenbildung und Einknicken dünnwandiger Rohre beim Biegen [Prevention of Wrinkling and Buckling of Thin-Walled Tubes During Bending]” by Prof. Dr.-Ing. G. Öhler, Bad Dürkheim). “Thin-walled” is understood in this context to mean tubes whose wall thickness is small in relation to the diameter and the bending radius, for example, tubes having a wall thickness of approximately 0.8 mm at a diameter of approximately 80 mm and a bending radius of approximately 120 mm. In order to keep the problems of wrinkling and deviation from a circular profile, which arise during bending of such tubes, as small as possible, the tube has been supported on its inner wall over the entire length of the bending curve using mandrels fixed axially in the tube. Therefore, there are mandrels supporting the tube over the entire bending curve which have a bendable section in the form of helical springs having turns pressed tightly together or in the form of ball links which form a link chain (U.S. Pat. No. 4,481,803). Both types of mandrels have the disadvantage that the tube to be bent is not supported over its complete surface in the region where the tube is bent. Most critical is the incomplete support on the inner curve, where wrinkles may form. With linked mandrels made of ball links, gaps are present from the beginning on the inner curve, so that the danger of wrinkling is particularly great for them.
A further problem in the known bending devices is the clamping of the beginning of the tube. Support on a rigid cylindrical mandrel head is problematic, because such a mandrel head, which requires a relatively large clamping length for fixed clamping of the tube, cannot be pulled back through the bent tube.